Although he could be extraordinarily arrogant, the result of a tremendous self-belief and a well-justified confidence in his own intellectual powers, Arthur Cockfield was also immensely persuasive; and the sheer length of his career as an adviser on tax packages to the Conservative Party is tribute to the enormous value put on his advice.

Even before he became a leading adviser to the party, he had already had a distinguished civil-service career, mainly with the Inland Revenue, and, gravitating to the private sector, had risen to be managing director of Boots. He was 62 and a peer before he became a front-line politician, serving as Minister of State at the Treasury, 1979-82, as the last Trade Secretary before the office was subsumed in the Department of Trade and Industry, 1982-83, and finally as Chancellor of the Duchy of Lancaster, 1983-84.

Margaret Thatcher then ordered him to Brussels as Vice-President of the European Commission, a free- market counter-balance to Jacques Delors, whom she had reluctantly accepted as President. The two men worked well together and Cockfield was instrumental in persuading Delors to put the creation of a single European market ahead of plans for a single currency. The Single European Act of 1985, although not solely the product of Cockfield's drive and imagination, was the crowning achievement of a long and highly successful career.

Francis Arthur Cockfield never knew his father, Lt C.F. Cockfield, who was killed at the Battle of the Somme in August 1916, the month before his birth. Arthur was educated at Dover Grammar School and the London School of Economics, where in addition to his BSc (Econ) he obtained an LLB. He joined Customs and Excise in 1933 and claimed to have been the author of PAYE. From 1945 he was Director of Statistics and Intelligence and served as a Commissioner of the Inland Revenue, 1951-52.

In 1953 he left the Civil Service to become finance director of Boots, from 1961 its managing director. In 1962 he was appointed to the National Economic Development Council, serving until 1964 and he also served on the Council of the CBI.

He was then drawn into Edward Heath's policy exercise for the Conservative Party and was the most active member of the group looking at taxation. He came up with an imaginative scheme for a wealth tax that would replace other forms of taxation on capital, but it proved unacceptable to the Shadow Cabinet. Nevertheless his advice and expertise continued to be valued and he was a major architect of the proposals that went into the final report and which were implemented by Tony Barber in the 1971 and 1972 Budgets. By then Cockfield had been appointed Adviser on Taxation Policy to the Chancellor of the Exchequer.

When the Heath government decided that it must control both prices and incomes as a means of controlling inflation in face of entry into the EEC, Cockfield accepted the chairmanship of the Price Commission in 1973. It was some measure of the climate of the times that both Cockfield and the minister to whom he worked, Geoffrey Howe, were free-marketeers and proto-monetarists, driven by the apparent urgency of the situation to compromise their beliefs.

Cockfield resumed his role as an adviser to the Conservative Party as a key member of the Economic Reconstruction Group that Howe as shadow Chancellor set up to consider public expenditure, tax reform and economic strategy. When the Conservatives returned to power in 1979, Cockfield, who had been given a peerage in 1978, became Minister of State at the Treasury, taking charge of the Inland Revenue and leaving his mark on tax-reforming budgets.

Howe as Chancellor came to treat Cockfield as "a uniquely valuable, all-purpose 'mobile' reserve" until in 1982 he was appointed to the Cabinet in his own right as Secretary of State and President of the Board of Trade. He spent little more than a year there before the department was merged with Industry. After the general election in 1983, Cockfield was made Chancellor of the Duchy of Lancaster, but after 15 months he stood down to go to Europe as the Vice- President of the European Commission.

Cockfield was unsure whether he wanted the job and had to be persuaded by his wife to take it. It was to be the crown of his career. While it may be wrong to see it as a critical turning-point in the history of the EEC, there is little doubt that the single-market initiative with which Cockfield was closely identified changed the context in which many other policies were to be shaped and drew other countries towards membership of the European Community. The move which he and Delors engineered restored momentum to a community that was at risk of stagnating.

In the round of consultations that Delors had undertaken with member governments, he had offered four options to relaunch the community: institutional reform, monetary union, closer co-operation in defence or an economic revival based on completion of the internal market. His personal preferences favoured the first two, but the last attracted the greatest degree of consensus; Delors was still hankering after monetary union as late as April 1985.

In the carve-up of responsibilities at the start of the Commission, Cockfield persuaded Delors to give him not only the internal market portfolio, but also financial institutions and company taxation, the customs union and indirect taxation, and he also fended off the formation of explicit policy linkages between his programme and those proposed by other Commissioners. It was a remarkable "land grab" and it enabled Cockfield to put his own stamp on the single-market initiative.

He was influential in the decision to lay down a deadline of 31 December 1992 for the completion of the market; and can also be credited with persuading Delors to adopt the high-risk strategy of framing a full single-market programme in advance, rather than allowing it to emerge piecemeal: as Cockfield recalled,

It was essential that we had a properly structured programme covering all the vital elements of the internal market. It was no good proceeding as previous Commissions had done by picking out subjects that happened to catch the eye of particular member states. It had to be the lot.

In the brief interval between the Brussels (March 1985) and Milan (June) meetings of the European Council, Cockfield and Delors managed to produce a massive, detailed, but elegantly shaped programme of no fewer than 283 measures which they thought necessary to the operation of a "frontier-free Europe". It was prefaced by a statement of the underlying philosophy and every single proposal had its own time schedule attached.

Well aware that, by moving quickly, he could shape decisively the way others conceptualised the single-market project, Cockfield claims that "it was the sheer speed with which I produced the White Paper that allowed 'the tide' to be taken at the flood". The immodesty is not uncharacteristic, but probably justified, as is his claim that, by publishing the White Paper two weeks before the European Council, he hoped to "give heads of government sufficient time to read the document and appreciate the immense importance of the opportunity being opened up" but not to "give their officials enough time to pick it to pieces".

The rapid preparation and launch of the White Paper at a press conference successfully shaped the policy agenda and locked governments into considering something definite. Almost certainly, however, the key proposal that ensured success was the adoption of qualified majority voting on all measures envisaged by the Single European Act. Close on 300 had been envisaged and by 1992 90 per cent had been embodied in European legislation.

Cockfield's later efforts to move towards harmonising indirect taxation in particular met with opposition, particularly from Nigel Lawson, and it was not a great surprise when Thatcher decided not to appoint him for a second term. Cockfield was furious. Instead he took up an appointment with Peat Marwick McLintock as an adviser on European affairs, 1989-93, but as a patron of the Federal Trust he continued to contribute to the public debate, co-authoring Network Europe and the Information Society (1995) and re-issuing his earlier call to complete the internal market, Europe without Frontiers (1988), in a revised form. The European Union: creating the single market (1994) was his own account of the making of the Single European Act.

In the House of Lords he was in general a loyal supporter of the Conservative cause, arguing strongly for the enlargement of the European Union, but in his last years he became an advocate of an 80 per cent-elected chamber.

Cockfield was a man of formidable intellect, but inclined to be dismissive of other people's ideas if they ventured into fields that he regarded as his own. Lawson tended to keep him at arm's length but earlier Conservative Chancellors valued what Tony Barber described as "his experience and inventive mind". Howe has described him as "a polymath" while his chef de cabinet in Europe, Andrew Cahn, thought him "a phenomenal organiser and a phenomenal brain". His exceptional memory and mastery of detail underpinned the broad sweep of his ideas and in their pursuit he displayed both zeal and quite exceptional tenacity.

Thatcher began as a great admirer and for a brief period he managed to get on well with her as well as with Delors, a man with whom he had a remarkable affinity. But she came to think he had gone native. In fact she was greatly mistaken in thinking him "a natural technocrat of great ability and problem-solving outlook".

Apparently a pragmatist, he was in fact "a cool Cartesian whose logic is so deadly that he can push systematically to extremes. You need that kind of mind to work through the consequences of abolishing frontiers," the European civil servant Michael Petite thought; and in pursuit of that logic Cockfield became as much an ideologue as Margaret Thatcher where Europe was concerned.